Divalent cation effects on lens conductance and stretch-activated cation channels

Area of Science:

• Ocular Physiology
• Membrane Biophysics
• Ion Channel Function

Background:

• The frog lens epithelium is crucial for maintaining lens transparency and function.
• Ion transport across the lens epithelium is vital for its optical properties.
• Stretch-activated ion channels are implicated in cellular responses to mechanical stress.

Purpose of the Study:

• To investigate the properties of ion channels in frog lens epithelium.
• To determine the role of stretch-activated cation channels in lens physiology.
• To examine the effect of extracellular divalent ions on lens cell and whole lens electrophysiology.

Main Methods:

• Patch clamp recordings of single channels from isolated frog lens epithelial cells.
• Electrophysiological measurements on intact frog lenses and single voltage-clamped epithelial cells.
• Systematic removal and reintroduction of extracellular divalent ions, particularly calcium.

Main Results:

• A stretch-activated cation channel, selective for cations over anions, was identified in frog lens epithelium.
• Removal of extracellular divalent ions significantly increased lens cell and whole lens input conductance.
• Extracellular divalent ion removal depolarized the intracellular voltage of the intact lens.
• Divalent ions blocked conductance and voltage changes in a manner consistent with stretch channel properties.

Conclusions:

• Stretch-activated cation channels show functional similarities to the changes observed in lens conductance and voltage upon removal of extracellular divalent ions.
• Despite parallels, direct evidence for the opening of these channels under conditions of divalent ion removal remains elusive.
• Further research is needed to fully elucidate the role of these channels in lens electrophysiology and their activation mechanisms.